After a restless night, Harry awakens to chaos: everyone is racing around, trying to pack as quickly as possible. The Advance Guard is accompanying Harry and the others to King’s Cross Station, and Sirius insists upon coming along in his dog form, much to Mrs. Weasley's dismay. They wait for Sturgis Podmore, who is late, but eventually move on without him. Sirius, who has been confined until now, scampers around and snaps at pigeons.

After bidding everyone goodbye on the platform, Harry, Ron, Hermione, Fred, George, and Ginny board the Hogwarts Express. Fred and George depart to talk business with Lee Jordan. When Harry suggests finding a compartment, Hermione and Ron awkwardly explain that they must join the other prefects for instructions, but promise to return soon. Harry and Ginny search for an empty compartment; Harry notices that everyone is looking at him, then remembers that the Daily Prophet has been calling him a lying madman all summer. They meet Neville, and Ginny leads them into a compartment. Inside is an odd-looking girl reading a magazine upside down. Ginny introduces her as Luna Lovegood, a Ravenclaw student. Their discussion turns to Neville’s birthday present, a rare Mimbulus Mimbletonia plant. He pokes it with his wand to show its defence mechanism, and the entire compartment is sprayed with horrid-smelling green pus just as Cho Chang walks in to greet Harry.

An awkward moment passes. Cho leaves and Ginny cleans the stinksap off them. Ron and Hermione return to announce that Draco Malfoy and Pansy Parkinson are the Slytherin Prefects; Ernie Macmillan and Hannah Abbott are Hufflepuff Prefects; and Anthony Goldstein and Padma Patil represent Ravenclaw. Ron tells a bad joke, at which Luna laughs inappropriately loudly. Harry notices Sirius Black's name on Luna's magazine cover. He asks to borrow the magazine, and reads an article claiming Sirius is actually a singer before realizing the story is bogus. Hermione disdainfully states that the Quibbler is "rubbish," to which Luna replies, "My father’s the editor."

Draco Malfoy and his ever-present sidekicks, Crabbe and Goyle suddenly appear. Draco snidely asks Harry how it feels being second to Ron, and hints that he recognized Sirius at the train station. Hermione orders him out, but after he departs, Harry and Hermione exchange troubled looks. With Luna and Neville there, they are unable to say anything, and Ron seems oblivious to this exchange.

They reach Hogwarts, but rather than Hagrid’s familiar voice greeting the first-years, they hear Professor Grubbly-Plank. They hardly have time to ponder this before Ginny and Harry have to carry their belongings to the carriages. Harry is stunned that the carriages are no longer horseless; they are drawn by black, skeletal horse-like creatures with leathery skin and wings. Ron sees nothing, leaving Harry wondering if he has gone mad. Luna approaches, saying she also sees them, leaving Harry confused: is confirmation from someone believing in Crumple Horned Snorkacks truly reassuring?

There are several interesting developments in this chapter. Sirius demanding to see Harry off at the Hogwarts Express is reckless and puts him at risk of capture, and we see that it endangers Harry and his friends, and could possibly expose the Order of the Phoenix. His dog Animagus form may also have been recognized by the Malfoys, which could lead to Harry, and possibly Dumbledore, being accused as his accomplices. His impulsive act suggests that Sirius' judgment may be deteriorating.

It is not immediately apparent how Draco and Lucius would have recognized Sirius. However, we must recall that Peter Pettigrew (Wormtail) started working for Voldemort fifteen years ago, and before that was Sirius' close friend at school. Wormtail can describe Sirius' Animagus shape to Voldemort, and Voldemort, knowing that Sirius would likely be in the Order of the Phoenix, would pass on that information to his returned Death Eaters, including Lucius Malfoy. It does not seem to occur to Sirius that his Animagus form may be recognizable by Voldemort's organization.

On the train, Harry must fend for himself for a while, as Ron and Hermione report for their Prefect duties. Still smarting a bit over Ron's new status, Harry is embarrassed to find himself seated with some less popular students, those labeled "misfits" by other students. Luna Lovegood, in particular, is an oddity Harry would rather avoid, though Ginny seems on friendly terms with her. Harry does have his first inkling that Cho Chang, who he has had a crush on for some time, appears to show an interest in him, though she catches him at a rather awkward and embarrassing moment. However, Harry, like Cho, is still deeply affected by Cedric Diggory's death, and pursuing a relationship may be an unwise course for either at this time.

Harry recognizes the issue of the Quibbler as the same one that Kingsley Shacklebolt had earlier slipped to Mr. Weasley, saying it would amuse Sirius. We now know exactly why Sirius would be amused.

Hagrid's absence is not entirely unexpected; Harry knows he is on a secret mission for Dumbledore. But Harry considers Hagrid as family, a representation of comfort, security, and familiarity, and so his continued absence is unsettling. Harry is also worried for his friend's safety, despite his large size and apparent invulnerability.

Intermediate warning: Details follow which you may not wish to read at your current level.

The strange, horse-like creatures pulling the carriages are Thestrals, and they are only visible to those who have seen death. Until now, Harry, like many other students, believed the carriages magically pulled themselves. He sees the Thestrals now because he witnessed Wormtail (Peter Pettigrew) murdering Cedric Diggory. Luna Lovegood, a most unusual girl anyway, sees them because she was present when her mother accidentally killed herself experimenting with magic. They are also visible to Neville Longbottom, though he mentions nothing about it here. We learn later that he once saw a relative die. His first encounter with them, therefore, would have been in his and Harry's second year; as Harry and Ron arrived in the flying car that year, they were absent when Neville first saw the Thestrals. By now he may consider them commonplace, and may even be unaware that they are invisible to others. Curiously, we will later discover that most other students seem oblivious to Thestrals' existence, indicating that those who can see them perhaps rarely mention them. Despite being gentle creatures, they are painful reminders of death to those who witnessed someone dying. More is learned about these unusual creatures in Hagrid's Care of Magical Creatures class, and they will have a role to play later in the book and in the series.

It could be argued that although Harry is unable to see the Thestrals until after Cedric Diggory was murdered, he, technically, had witnessed other deaths prior to this tragic event. Close examination of the events suggests otherwise, however. In Chapter 1 of Harry Potter and the Goblet of Fire, Harry "sees" the Muggle, Frank Bryce, being killed by Voldemort. However, Harry was not physically present when Frank was slain. Harry instead watched the death through a mental connection he has to Voldemort. Though what he viewed was apparently real and from his own perspective, he was unaware it was actually happening at the time, and merely passed it off as a bad dream. This may be why the Thestrals remained invisible to him

We discover later that Professor Quirrell died when Voldemort abandoned him in the first book. Harry was present, but, being unconscious, he never saw Quirrell's death.

Finally, Harry was present when Voldemort killed his mother, and when Voldemort's killing curse rebounded on him. The author has explained that Harry's cot (baby crib) blocked him from witnessing his mother's death, nor could he have comprehended anything he did see at so young an age. Additionally, Harry may not have seen Voldemort being hit by his rebounding course, nor was Voldemort really quite dead.

We are never positive that the Malfoys recognized Sirius in his dog form, but on the train, Draco hints to Harry that they did, and a story in the Daily Prophet placing Sirius in London will appear shortly.

Not only is Harry miffed when Ron and Hermione are off performing their prefect duties, he is also embarrassed to be seated with unpopular students like Neville Longbottom and Luna Lovegood. These two "misfits", however, will prove to be among Harry's strongest and most capable allies. Neville will also be closely associated to a prophecy regarding Voldemort and Harry, and Harry will learn they have actually much in common.

Sturgis Podmore's absence is because he was arrested the night before while attempting to enter through a locked door at the Ministry. Evidence will suggest that this doorway leads to the Department of Mysteries, home to an artifact (which the Order had called a "weapon" when talking about it with Harry) which Voldemort greatly desires. Lucius Malfoy, at Voldemort's orders, had been attempting to compel other wizards to enter the Department of Mysteries and recover that item; as this is what Broderick Bode was later forced to do, we can only guess that the same fate has probably befallen Podmore. The irony of Podmore, given the mission of protecting the artifact, having been compelled to attempt to steal it for Voldemort, is not missed by the mature reader, but we suspect that it was not intentional on Voldemort's part, no matter what the author's intent was. Voldemort and Lucius may not be aware that the Order is already operational and on guard.

That Luna's father publishes the Quibbler will also prove important, as this will provide Harry a direct channel for disseminating truthful information about himself and Voldemort without it being censored or filtered through the establishment media, namely The Daily Prophet. The Prophet, in this and later books, will be forced to toe the Ministry line, and we will witness the effect that it has on Harry. It soon becomes vital for Harry to have another means to truthfully tell his story. The Quibbler's contrarian nature will again prove to be important in the series' final book.

This is the first mention of any Wizarding alternate press. The Quibbler will be useful in this book when Hermione determines that Harry needs to get the true story out to the public; Harry's interview with Rita Skeeter will run in the Quibblerin this book. The Quibbler will also appear in the final book, where it is noted that Xeno Lovegood is publishing the truth about Harry because it seems to sell more papers than stories about Snorkacks. This will also result in Ron's suggestion that the Trio visit and speak with Xeno shortly after Christmas, which results in the reader hearing the Story of the Three Brothers.

Neville's plant, the Mimbulus Mimbletonia, is clearly a signal that he is showing ability with magical plants. We will see this again later in this book, and he will be assisting Professor Sprout with the plant-based defence of Hogwarts in the climactic battle.

The Twins talking business with Lee Jordan is a clear precursor to the establishment of Weasley's Wizard Wheezes. While we saw the beginnings of this in the previous book, it would only have become a solid expectation with Harry's backing. They will be testing products throughout this book, will establish a physical store in the next, and will continue their business by mail order in the final book.